MANCHESTER UNITED'S injury problems are mounting up with Chris Smalling likely to be sidelined until after Christmas.

Smalling sustained a groin injury early into the 2-1 win at Southampton on Monday night and scans have confirmed muscle damage that will keep him out for at least a fortnight.

It leaves Manchester United manager Louis van Gaal facing another defensive re-shuffle ahead of Sunday's clash with Liverpool at Old Trafford.

The absence of Smalling, who has already missed the best part of two months through injury this season, means Jonny Evans is likely to start alongside Marcos Rojo in the centre of defence.

Evans made his first appearance since September when replacing Smalling at St Mary's. Michael Carrick is another option as United look for a sixth successive win.

The England midfielder was also pressed into emergency defensive duties after Paddy McNair was hauled off having struggled in a three-man unit.

With McNair certain to be left out and Phil Jones still unavailable, van Gaal, may revert to a flat back four against Liverpool.

He could recall the fit-again Rafael at right-back although Luke Shaw's ankle injury is delaying his return on the left side of defence.

Smalling's injury setback means the Dutchman has endured 43 separate injuries to his side this season.

United's Boxing Day clash with Newcastle would appear to be the earliest date for a possible return for the England international, although van Gaal has consistently shown he is not keen to rush players back into action.